In U.S. Pat. No. 7,159,687 (Dunn) issued Jan. 9, 2007 and assigned to the present Assignees is disclosed a hydrostatic agricultural tractor used as a self-propelled swather tractor. This uses the typical construction for such tractors which has front ground wheels mounted on the frame at fixed angles parallel to each other and parallel to a center line of the frame and rear ground wheels mounted on a respective castor. Each of the front ground wheels is driven by a respective drive motor which allows variable speed in both the first and second directions such that steering of the tractor is effected by a differential in speed between the front wheels with the rear wheels following the steering in a castoring action. The disclosure of this patent is hereby incorporated by reference or may be referred to for further detail not disclosed herein.
Such hydrostatically driven tractors used primarily for swathing are commonly used and readily available. The tractor carries at a forward end on suitable sprung supports a header for cutting standing crop with the crop being transported on the header to a suitable discharge location generally centrally of the tractor for forming a swath in the field from the cut crop.
Such tractors generally include a pair of front wheels just behind the header which are fixed to the frame of the tractor so that they remain at an angle parallel to each other and parallel to a center line of the tractor. The tractor is supported at the rear end by a pair of castor wheels which are attached to a cross axle pivotally connected to the frame at a center horizontal pivot point, commonly known as a walking beam. The axle is supported relative to the ground the castor wheels at the ends of the rear axle so that the wheels trail behind a vertical pivot mount for the wheels and are free to swivel through 360° around the pivot mount.
The front wheels only are driven and are driven in a manner which allows full control in the forward and reverse directions so that steering is effected by a differential speed between the two front wheels with the rear wheels following in the conventional castoring action.
Typically compression of the formed swath is required for fluffy crops which can blow away in windy conditions such as canola and flax and such compression is provided by swath rollers towed behind the swather tractor to apply pressure onto the swath as after it is discharged from the rear of the tractor.
An example is shown in Canadian Patent No: 599,761 issued Jun. 14, 1960 by Hellegards which shows a simple cylindrical roller attached behind a towed swather.
Many manufacturers have provided towed swath rollers which comprise a wheeled frame with a forwardly extending hitch pole which attaches to the rear of the swather tractor. One example is shown in a brochure by the present Applicants where a transverse beam carried on the ground wheels has a pair of rearwardly extending arms between which is mounted a metal roller drum. The drum has a cylindrical center section with flared frusto-conical ends. The height of the drum can be adjusted on the frame to adjust the pressure on the swath, depending on the thickness of the swath. The ends of the drum can be closed by circular end plates.
This type of swath roller has achieved considerable success and many have been sold by various manufacturers.
More recently the metal drum has been replaced by a plastic rotationally molded drum. This has advantage that it does not rust and can be manufactured cheaply but it has disadvantages that it slips on the crop and therefore may not properly rotate in a rolling action. Also the drum is very light so that it may not apply the required pressure.
Swather tractors have in recent years become much larger and more complex with some having independent suspension of the rear wheels. Such tractors are of the type with front wheels which are independently driven to provide a steering action together with castor rear wheels which follow the direction determined by the differential speeds of the front wheels. The towed swath rollers have become inadequate to provide a suitable convenient arrangement for the operator. At the same time there has been an increased demand for swath compression.
There are a number of problems with prior art rollers:
Poor visibility to rear of machine in field and on the road in cab forward mode as disclosed in Dunn above.
Poor visibility to front of machine on the road in engine forward mode.
Roller obscures the rear lights in the field.
Use of a roller with flared ends (different diameter from center section to outer sections), tends to be driven by the end sections which causes scrubbing at the center section since it has a slower peripheral speed. This can cause the crop to be disturbed with some of the heads flipped up out of the windrow and leave it vulnerable to wind and shattering.
The use of a forming device under the tractor will act to push into the windrow when the machine reverses.
A larger roller diameter is not practical due to poor visibility, weight etc.